Sympatric, Allochronic Populations of the Pine White Butterfly (Neophasia Menapia) Are Morphologically and Genetically Differentiated
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Allochronic isolation remains an understudied, and potentially under-appreciated, mechanism of reproductive isolation. Allochrony has been detected in two sympatric populations of the pine white butterfly (Neophasia menapia); a typically univoltine species found throughout Western North America. At two sites in California there are early and late flights. Differences in flight time are accompanied by differences in wing shape and pigmentation. A combination of morphological analysis and population genomics was used to assess population differentiation at both sites with sympatric populations. Differences in wing shape and pigmentation between early and late flights were quantified. Pigmentation was significantly different at both sympatric sites, while shape was significantly different at just one of the sites. 20,737 SNP’s, obtained using next generation sequencing, were used to calculate pairwise FST’s. FST between early and late flights was significantly different from zero at both sympatric sites. The hypothesis of a double invasion from Sierra Nevada sites to Coastal Range sites, leading to the two flights at sympatric sites, was rejected. Allochrony is likely to have arisen in sympatry, from within the Coastal Range.